1. Field of the Invention
The present invention relates to a radio transceiver station, a redundantly operable industrial communication system and method for operating the communication system.
2. Description of the Related Art
An industrial automation system usually comprises a multiplicity of automation devices networked to one another via an industrial communication network and is used to control or regulate installations, machines or devices within the scope of manufacturing or process automation. On account of time-critical framework conditions in technical systems automated using industrial automation systems, real-time communication protocols, such as PROFINET, PROFIBUS or real-time Ethernet, are predominantly used for communication between automation devices in industrial communication networks.
Interruptions in communication connections between industrial automation devices or computer units of an industrial automation system are extremely problematic. In addition to a loss of information, this may result, for example, in disadvantageous repetition of transmission of measurement or diagnostic results or service requests. This causes additional utilization of communication connections of the industrial automation system which, in turn, may result in further system faults or errors.
In addition, untransmitted or incompletely transmitted messages may prevent an industrial automation system from changing to or remaining in a safe operating state, for example. In the worst-case scenario, the result may be failure of a complete production installation and costly production downtime. A particular problem regularly results in industrial automation systems from message traffic with a comparatively large number of, but relatively short, messages, thus intensifying the above problems.
In order to be able to compensate for failures of communication connections or devices, communication protocols for the bumpless redundant transmission of messages in highly available industrial communication networks have been developed. These include High-availability Seamless Redundancy (HSR) and Parallel Redundancy Protocol (PRP) which are defined in the Industrial Electrotechnical Commission (IEC) 62439-3 standard and, in the case of network faults, make it possible to transmit messages without a changeover bump with extremely short recovery times. According to High-availability Seamless Redundancy and the Parallel Redundancy Protocol, each message is duplicated by a transmitting communication device and sent on two different paths to a receiver. Redundant messages representing duplicates are filtered out of a received data stream by a communication device at the receiver end.
The IEC 62439-3 standard has previously prescribed exclusively wired transmission paths for the Parallel Redundancy Protocol (PRP) on account of relatively long latency delays in wireless communication systems and a non-deterministic transmission behavior caused thereby. Suitability of WLAN transmission paths in PRP communication networks is investigated in “Towards a Reliable Parallel Redundant WLAN Black Channel”, Markus Rentschler, Per Laukemann, IEEE 2012. Parallel application of various diversity techniques for space, time and frequency, for example, can be used to compensate adequately for effects of stochastic channel fading in WLAN communication networks.
EP 2 712 124 A1 discloses a redundantly operated industrial communication system having communication devices redundantly connected to an industrial communication network, in which messages are transmitted wirelessly at least in sections. A plurality of buffer storage units for message elements received in a wired manner at a network node and for message elements to be wirelessly transmitted by the latter are provided in the industrial communication network. If a maximum buffer size is exceeded, an oldest message element in the respective buffer storage unit is deleted. Until the maximum buffer size is exceeded, the oldest message element is selected as the next message element to be wirelessly transmitted.
DE 10 2012 209509 A1 describes an apparatus for securely transmitting data between a mobile subscriber having at least one transmission apparatus and a stationary receiver. Here, the mobile subscriber can change between a plurality of radio cells. Each radio cell has at least one transmission apparatus that is connected to at least one network in a wired manner. The stationary receiver is likewise connected to the at least one network in a wired manner. Both the wireless transmission between the mobile subscriber and his respectively associated transmission apparatus and the wired transmission of data between the transmission apparatus and the at least one associated network are carried out in a redundant manner. The stationary receiver is connected to the network in a redundant and wired manner.
In order to connect automation devices having completely independent Ethernet interfaces within a redundant communication network to singly connected automation devices in a highly available manner, a Y switch is used for the respective singly connected automation device according to DE 10 2013 211406 A1. Here, the Y switch is connected to a first or second subnetwork of the redundant communication network via a first or second port, while it is directly connected or indirectly connected via a third port to the singly connected automation device. In addition, incoming data frames at the first, second and third ports are assigned to a first, second and third VLAN, respectively. In addition, the first and second ports are set up as untagged members for the first and third VLANs or for the second and third VLANs. The third port is set up as an untagged member for all three VLANs. Unicast MAC addresses learnt at the first two ports are automatically adopted as a static entry for the third VLAN. If a unicast MAC address learnt at the first two ports is deleted, the corresponding static entry for the third VLAN is also deleted.